The present invention is directed to novel adhesive compositions which may be characterized as possessing resistance to degradative environmental forces such as ultraviolet light (UV) and oxidation, are tacky to the feel, i.e. possess "perceived tack", have good shear resistance, are cost-efficient and can be processed into adhesive tapes by calendering as well as by other per se known coating means, e.g. solvent casting or extrusion coating.
Various adhesive compositions are known which possess some but not all of the above characteristics.
For example, so-called S-I-S adhesives having polystyrene end blocks and an isoprene midblock make excellent adhesives. However, due to the unsaturated isoprene midblock, they are not resistant to UV or oxidation. Accordingly, they are not useful for such applications as storm window tapes where they would be subjected to UV.
On the other hand, polyisobutylene adhesive formulations are essentially saturated and consequently are resistant to UV and oxidation. However, because they have minimal unsaturated hydrocarbon groups, they are not readily modified, e.g. by crosslinking, to provide acceptable shear resistance.
The acrylic aamily of adhesives combines the properties of resistance to shear, UV and oxidation. However, they are costly and cannot be made into adhesive tapes by calendering, a particularly efficacious coating means in the tape manufacturing art.
Relatively recently in the adhesive art, much attention has been focused on a class of adhesives designated as S-EB-S which are thermoplastic rubbers having polystyrene end blocks and rubbery ethylene-butylene midblocks. The ethylene-butylene midblocks are regarded in the rubber industry as being saturated due to the presence of minimal unsaturated hydrocarbon groups. Consequently, the S-EB-S elastomers should in theory obviate the above-noted problem of the unsaturated isoprene midblock in S-I-S adhesives and provide an adhesive having the requisite UV and oxygen stability. However, as will be detailed in more particularly hereinafter, they are not tacky and attempts to incorporate the usual tackifiers, i.e. those which are cost-effective and consequently commonly employed in the adhesive art, failed to provide an adhesive which possesses perceived tack or has tack measurable by conventional instrumentation, e.g. the Polyken (trademark of The Kendall Company) probe tack instrument.
Having failed to obtain an S-EB-S adhesive having the requisite tack, Applicants then theorized that what was needed was an elastomeric component having a shorter chain. Based upon this assumption, they then blended the diblock copolymer, polystyrene-poly(ethylene-butylene) (S-EB) with S-EB-S in various amounts ranging from 20-75% S-EB along with equivalent amounts of tackifier. While the resulting composition was slightly better in terms of perceived tack, there was still no measurable tack.
The task of the present invention in essence can be said to be to solve the aforementioned problems and thus provide an adhesive formulation which, as mentioned above, has the requisite stability against UV and oxidation, possesses the desired adhesive properties of acceptable levels of tack and resistance to shear, is cost-efficient and can be applied to a suitable backing material to an adhesive tape by calendering as well as by the other known coating means such as solvent casting or extrusion.